Chemistry

Aviation Technology Understanding Jet Engine Metallurgy



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The engines roar, the vibration in the passenger compartment can be felt.  We are depending on this big mass of metal to take us to our destination safely.  What goes into making our journey safe?

 A jet engine takes about two years to build.  Its design is essential and it uses the finest materials available.  The metals have to withstand heat.

 Let’s look at how the model works.

1. Think of the shape of a clam but as large as an automobile hood.  When you open the hood, like a clam, the hood goes all the way around to create a secure little container.  This is the "cowling".   The design makes it easy to check the inside of the engine.

2.  There are four engines.  Each is attached to the wing of the plane with individual tubes called pylons.  These pylons are hollow.  The pylons are able to intake the fuel to the engine.

The materials that most jet planes use in manufacturing have to be strong, rust proof and must be heat and cold stable.  Titanium, which was first used in engines in the 1950s, is still used today.  The hardness of titanium makes it extremely difficult to manipulate. Titanium, today, is a mixture with other metals, such as, aluminum or nickel.   Those roaring fans at the front of the engines have to be strong.  That is why they use titanium for the fans.  Birds, whooshed up through the fan, will not break the blades.

There are 25,000 plus parts to build a jet engine.  The way engineers use metal in the different parts of the engine:  Each section is done separately before attachment to the plane.

FANS, which are in front of the engine, are made of molten titanium.  To make the fans stronger a honeycomb form of titanium is placed in the cavity.

COMPRESSOR DISC looks like a notched wheel (think of the inside workings of an old watch where the two notched wheels work together to make the clock work).  The compressor disc has the blades attached to it.  This disc has to be strong, as well as accurate.  This is where “powder metallurgy” is used.  This works by pouring molten metal into a turntable.  The turntable rotates at a high speed and the metal breaks into small pieces.  The molten metal that broke off into small pieces cools so fast that it turns into a pure powder.  The powder is placed into a vacuum mold forming case.  The powder, heated under pressure, turns the disc into its shape.  It is bolted to the blades.

COMPRESSOR BLADES have not changed since the introduction of jet engines.  The blades are made by placing them into a ceramic mold, then heated in a furnace, and the excess cut off.

COMBUSTION CHAMBERS are small and withstand extreme heat.  Once again, titanium is mixed with a compound to be formed into ducts.  After they cool, they are welded together and placed on the engine.

TURBINE DISCS AND BLADES:  When the compressor disc was made, they used powder metallurgy.  For the turbine disc, it is used again.  The difference is that they will make a wax mold for the blades.  After the mold, formed by the wax, is removed, molten metal is poured into the cavity the blades left.  They can now use computer regulated ovens in order to have the blades and turbine disc perfectly aligned.

EXHAUST PIPES are made of titanium and Kevlar.  They are molded together.

The whole plane assembled and tested is ready to fly.  After two years, you can jet your way across the world.  Bon Viree!

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